The development of brain biogenic amines, cyclic nucleotides and hyperactivity in 6-OHDA-treated rat pups

Developmental changes in the behavior and brain biochemistry of rat pups were investigated in rats administered intracisternal injections of 6-hydroxydopamine (6-OHDA) or its vehicle at 5 days of age. Although pups of both groups were equivalent in their activity at 15 days of age, 6-OHDA-induced hyperactivity emerged at 20 and 30 days of age in a between-group design in which rats were only tested at one age. Body weight measurements revealed that 6-OHDA-treated rats were underweight at 15, 25 and 30 days of age. Furthermore, at 20 days of age, total activity was inversely related to body weights in the 6-OHDA-treated pups. Whole-brain levels of dopamine (DA) were decreased at every age by the 6-OHDA treatment, whereas norepinephrine (NE) levels were virtually unaffected by 6-OHDA at these same ages. Total activity was inversely correlated with whole-brain DA levels at 20 and 30 days of age when 6-OHDA-treated pups were hyperactive. Measures of cerebellar and "rest-of-brain" adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) were not uniformly altered by either the 6-OHDA treatment or by maturation. Results are discussed both in terms of brain biochemistry modulation of hyperactivity and the contribution of decreased body weights induced by 6-OHDA to the production of hyperactivity.